1. Field of the Invention
The present invention relates to a method for adjusting the wheel alignment of a vehicle, and particularly to a method for adjusting a wheel angle of a vehicle in which a wheel of a vehicle with a tire fitted thereto is rotated on a wheel rotating surface, the tire is deformed, and the forces thereby generated are measured, the wheel angle is then adjusted on the basis of the results of the measurement providing an improvement in the running stability of the vehicle and a reduction in the wear of only one side of the tire.
2. Description of the Related Art
In general, wheels are provided with a camber angle which ensures the running stability of the vehicle and are also provided with a toe angle for preventing wear on only one side of the tire caused by the camber angle (in the present specification, the term xe2x80x9cone-sided wearxe2x80x9d is used hereafter to describe a state where, upon observation of the state of wear of a worn tire, it can be seen that the amount of wear extending from one tread shoulder portion to the other tread shoulder portion changes in a tapered fashion, i.e. a state where one tread shoulder portion is more worn than the central portion of the tread and the other tread shoulder portion).
Conversely, the wheel may be provided with a toe angle for balancing the forces generated at the front tires and at the rear tires thereby ensuring the running stability of the vehicle and may be provided with a camber angle to prevent one-sided wear caused by the toe angle. Alternatively, the toe angle and camber angle may both be adjusted in combination to optimize the running stability of the vehicle and minimize the one-sided wear of the tire under the restraints imposed by the vehicle such as the structural dimensions thereof and the like.
Accordingly, in order to improve the running stability of the vehicle and resistance of the tire to one-sided wear during driving, it is necessary to adjust the toe angle and camber angle, which are the wheel angles (positional angles) provided to each wheel. In the conventional method of adjusting the toe and camber angle, generally, the angle and dimensions of each wheel are measured and the measured toe and camber angles are then adjusted so as to match the target values set when the vehicle was designed.
However, while tires have various characteristics such as ply steer, which is caused by the internal construction of the tire; toe force, which is generated because the tire is at an angle to the direction in which the vehicle is advancing caused by the fact that the direction in which the wheel is rotating is different to the direction in which the vehicle is advancing; self-aligning torque, which is generated because the direction of advancement does not match the point on the road-contacting surface to which the force is applied; camber thrust, which is generated when the tire deforms due to the camber angle of the wheel depending on the rigidity of the tire governed by the internal structure of the tire; camber moment, which is generated by the difference between the left and right sides of the road-contacting surface; conicity, which arises from manufacturing errors inherent in industrial products; and rolling resistance, which differs depending on the internal structure and the material used such as the rubber, these characteristics depend on and vary in accordance with the load applied to the wheel. Further, these characteristics also depend on the type of tire.
In other words, the above-mentioned forces are generated by the deformation of the tire. The force generated by the tire to control its running direction while causing the vehicle to advance is the sum of the above-mentioned forces. Therefore, regardless of the type of tire, this force differs depending on the load distribution of the vehicle to which the tire is fitted and the alignment of the wheel (wheel angle). Accordingly, to meet the demands for increased vehicle speed and better directional stability, a wheel alignment adjustment method is necessary which provides better running stability and one-sided wear resistance.
The technology disclosed in Japanese Patent Application Publication (JP-B) No. 51-18681 is known as a conventional adjustment method focussing on the characteristics of the tire. The wheel is driven using a plurality of rollers and each of the forces generated by the rollers is measured. The toe angle and camber angle are then measured on the basis of the direction and magnitude of the measured force. However, it has been verified that the force generated by the contact between the tire and the road differs depending on the configuration of the contact between the tire and the road surface. Because of this, the configuration of the contact between the tire and a roller are is very different from the configuration of the contact between the tire and the actual road surface. Therefore, the characteristics of the force generated differ greatly between the road surface and the roller.
More specifically, although the force generated using the roller resembles the lateral force caused by the ply steer and the provision of the toe angle when running on an actual road surface, the alignment and the size of the force are greatly different from those occurring when the wheel is run on an actual road surface. Moreover, the camber thrust is barely detectable. In addition, the forces generated in the tire arising from the deformation of the tire caused by external disturbances from the numberless bumps in the road surface cannot be detected.
Accordingly, In the above-described conventional art, the measured force exhibits values which are different from values obtained from an actual road surface. In order to correct the measured values to the values obtained from an actual road surface, data expressing the characteristics of the respective tires on an actual road surface is needed. Therefore the above-described conventional method lacks wide applicability in actual practice. Further, no technical information has been disclosed with regard to what angle the alignment should be adjusted to in order achieve the optimum alignment.
A technique is known in which a wheel is driven using a plurality of rollers which aims to achieve high running stability by bringing lateral forces to substantially zero (see Japanese Patent Application Laid-Open (JP-A) No. 7-5076). In this technique, a wheel which has a camber angle is given an alignment which generates a force in the opposite direction to the direction of the camber thrust in order to bring the generated lateral forces to zero.
However, even in this technique, in the same way as the previously described case, because the contact surface of the tire with the rollers is different from the contact surface of the tire with the actual road surface, the camber thrust is almost undetectable. Moreover, in order to offset the force generated by the rotation of the wheel so as to bring the lateral force to zero, it is necessary to apply the force from the road surface generated by the running of the vehicle in the opposite direction to the direction of the force generated by the vehicle. In this case, the deformation of the road-contacting surface of the tire becomes even greater than when the tire is in a stationary state, and this deformation of the road-contacting surface is a factor in the generation of one-sided wear of the tire.
A method has been proposed (see JP-A 8-334440) for adjusting the alignment of a wheel by rotating the wheel on a substantially planar surface using a belt or the like, detecting the force generated by the wheel and adjusting the alignment on the basis of that force. However, an actual road surface is formed with numberless bumps and hollows (protrusions and recesses) and a tire on a running vehicle is always deformed by these numberless bumps and hollows. The load applied to each wheel also varies when the vehicle is running over bumps and hollows of a comparatively long cycle also deforming each tire so that the tire on a running vehicle is rotating while being affected by the force generated by the contact of the tire with the road surface and the force from the above deformations. In contrast, the force which can be detected by rotating the tire on a planar surface formed from a belt or the like is only the force which is generated by the contact of the tire with the belt surface. There is additionally none of the load variation which is generated by an actual road surface with the result that only a portion of the forces generated by running on an actual road surface can be detected using the conventional method. Accordingly, even if the alignment of a wheel is adjusted on the basis of the forces detected in conditions which are unaffected by load variation such as those generated by a substantially planar surface, the running stability will be improved for a vehicle running on an extremely level surface, however, there will be no improvement in other running characteristics and in one-sided wear.
More specifically, when a tire is running on an actual road surface, forces are generated by different generating mechanisms. In spite of the fact that these forces differ depending on the characteristics of the tire, the following conventional methods have been used: (1) a vehicle is actually run using specific tires, the angle at which one-sided wear is the least without losing running stability is found empirically, and the wheel is adjusted to this angle; (2) the wheel is adjusted to angle where the force measured on a planar surface is offset to the minimum possible (substantially zero); (3) the wheel is adjusted to an angle where only the specific force measured by running the wheel on a planar surface or on rollers is the minimum possible (substantially zero); (4) the wheel is adjusted to an angle obtained through some other method. However, none of these methods can be applied to a variety of different vehicles running on a variety of different tires.
Moreover, the present inventors measured the lateral force and longitudinal force generated in a tire when the vehicle wheel travels over a step and proposed a method for adjusting the wheel angle of a vehicle in such a way that variation in the lateral force at the time the longitudinal force is at a maximum or substantially maximum value was at a minimum (see JP-A No. 10-7013). In this method, the longitudinal force is measured to detect the timing at which the deformation of the tire is at maximum and the period in which the longitudinal force is at maximum or substantially maximum is taken as the period in which the amount of tire deformation is at maximum or substantially maximum.
However, the timing at which the longitudinal force changes depends on the suspension geometry of the vehicle. The suspension geometry of the vehicle sometimes causes the timing at which the tire deformation is at maximum or substantially maximum to fail to match up with the timing at which the longitudinal force of the vehicle is at maximum or substantially maximum. Accordingly, the accuracy of the above-described adjustment method is affected by the suspension geometry of the vehicle and it is not always possible to adjust the alignment of the wheel to the optimum even if the above-described method is used.
Moreover, the vehicle""s steering (steer) characteristics, which have a great effect on the running stability of the vehicle, are determined by a balance between the forces generated in the tire on each wheel of the vehicle, and as the above-described technologies are all concerned with adjusting the wheel angle of individual wheels of a vehicle one by one, they give no consideration at all to the balance while the vehicle is running.
Moreover, a method in which, the size of the lateral force generated in the front and rear tires when the tires are rotating are compared, then steering characteristics (over steer, under steer, or neutral steer) is obtained in accordance with the distribution of the lateral forces and changes in the distribution of the lateral forces, is known. However, because the lateral force is a force is generated on the tire rotating on a flat surface in accordance with the wheel angle and the load, then even if the forces generated in actual vehicle are actually measured, it is difficult to apply the results to the adjustment of an actual vehicle.
Accordingly, even if the above-described technologies are used for adjusting the individual wheel angle, the problem remains that it is not guaranteed that the optimum steer characteristics will be obtained.
The present invention was conceived in consideration of the above facts and it is an object thereof to obtain a method of adjusting the wheel alignment of a vehicle in which an wheel angle can be adjusted to an wheel angle which accords with the characteristics of the tire such that the steer characteristics of the vehicle becomes substantially neutral.
The object of the present invention is thus to provide a method of adjusting the wheel alignment of a vehicle which enables the wheel angle to be simply adjusted to an wheel angle which accords with the characteristics of the tire and provides a running stability appropriate for an actual road surface, and at the same time reduces one-side wear and optimizes the running characteristics so that the steering characteristics are substantially those of neutral steer, without being affected by the suspension geometry of the vehicle.
When a tire is rotated by contact with an uneven road surface (a road surface having protrusions and recesses), the tire is deformed by load variations generated as the tire moves vertically relative to the ground-contacting surface of the tire and the lateral forces (specifically, the lateral force known as ply steer caused by the structure of the tire, the lateral force known as conicity caused by the manufacturing process, the lateral force due to the imparting of a slip angle (toe angle) to the wheel, and the lateral force known as camber thrust due to the imparting of a camber angle to the wheel) generated on the tire, by the deformation, all vary. In the technology disclosed in JP-A No. 10-7013, as was explained above, the angle of the wheel is adjusted on the basis of the variation in the lateral force generated in the tire when the deformation of the tire is at maximum or substantially maximum as the wheel travels over a step simulating an actual road surface (the variation in the load is occurred at the passage of the wheel over this step).
However, because the lateral force generated in the tire varies because of the deformation of the tire as the load changes or as the tire passes over step, as was explained above, then as the factors causing these deformations in the tire disappear, the tire, which had been in a deformed state, attempts to deform back to its normal shape and this deformation also causes the lateral force to vary. The present inventors, realized from the above facts, come to the conclusion that by observing the variation in the lateral force during a period including not only the time during which the deformation of the tire is at maximum or substantially maximum, but also the time during which the tire attempts to deform back to its normal state, and by adjusting the wheel alignment (adjusting the angle of the wheel) so that the energy of the variation in the lateral force over the above-described period is at a minimum, a higher degree of running stability suitable for an actual road surface and a further reduction in one-sided wear could be achieved.
In order to verify the above discovery, the present inventors performed the experiment described below. Specifically, a tire was rotated using a tire driving apparatus having, in at least one position on the tire-driving surface thereof in the direction in which the tire driving apparatus is driven to rotate, a planar protrusion whose length in the direction of rotation is long enough for the tire to sit completely thereon and whose length in the axial direction of the rotation which is orthogonal to the direction of rotation is larger than the width of the tire. (By this structure, a step is formed at the front and the rear of the planar protrusion along the direction of the rotation on the tire-driving surface.) The lateral force generated in the tire is measured repeatedly in short cycles. Then from the results of the measurement of the lateral force during each cycle (each measurement time) which is within a predetermined period which includes the time from the moment the tire is deformed as the wheel passes over the step until the tire rotates and substantially returns to its normal state, the sum of the square root of the rate of change (the value of the primary differential for the time of the lateral force) in the lateral force, as the energy of the variation in the lateral force within the above predetermined period, in each measurement time is repeatedly obtained while the alignment (in this experiment, the toe angle) of the wheel is altered each time by a predetermined amount.
FIG. 1 shows the relationship obtained by the above experiment between the toe angle and the energy of the variation in the lateral force generated in the tire within the predetermined period. As is clear from FIG. 1, the above experiment confirmed that a definite correlation exists between the toe angle and the energy of the variation in the lateral force. Confirmation was also made that when the toe angle of the vehicle was adjusted so that the energy of the variation in the lateral force was at the minimum, the running stability of the vehicle was improved greatly and one-sided wear was greatly reduced.
The present inventors also compared and evaluated the running stability of several different models of vehicle (vehicles 1 to 4) under two types of adjustment mode. One mode was with the wheel angle adjusted to the angle determined when the vehicle was designed (standard mode); the second mode, as in the experiment described above, was with the wheel angle adjusted so that the energy of the variation in the lateral force generated in the tire during a predetermined period including the time from when the tire is deformed by the wheel travelling over a step until the tire rotates and returns substantially to its normal state was at minimum (the present mode). The vehicles used as vehicles 1 to 4 all had a displacement of between 1600 cc and 3000 cc and had either an FF or FR drive system (i.e. passenger vehicles). The tires used were all models sold on the general market of a size appropriate to the vehicle to which they were fitted. The results of the experiment are shown in Table 1. The standards by which the results were evaluated are shown in Table 2.
As is clear from Table 1, the above experiment verified that, by adjusting the wheel alignment so that the energy of the variation in the lateral force generated in the tire during a predetermined period including the time from when the tire is deformed by the wheel travelling over a step until the tire rotates and returns substantially to its normal state is at a minimum, then regardless of the type of tire, the running stability of the vehicle can be greatly improved, and one-sided wear can also be greatly reduced. Moreover, even when the tire is deformed due to the load acting on the tire changing, the lateral force generated in the tire by the deformation of the tire shows the same change as when the tire is deformed by the wheel travelling over a step.
Accordingly, the present inventors realized, in the above experiment, by: rotating a wheel having a tire fitted thereto on a wheel rotating surface in a proceeding direction of the vehicle, measuring at least the lateral force generated in the tire when the tire is deformed either by the wheel on which the tire is fitted travelling over a step formed on the wheel rotating surface or by the load acting on the wheel being changed; determining (obtaining) the energy of the variation in the lateral force generated in the tire within a predetermined period, determining the optimum wheel angle in accordance with the characteristics of the tire on the basis of the above-determined energy of the variation in the lateral force; and adjusting the wheel angle to the above-determined optimum wheel angle, to obtain a running stability suitable for an actual road surface and achieve a reduction in one-sided wear.
The present inventors also realized that, because the steering (steer) characteristics of a vehicle are basically determined by the balance of the forces generated in the front and rear tires of a vehicle, if the wheel angle is adjusted so that the way in which the lateral force (or the rate of change in the lateral force: the primary differential value of the lateral force) changes, within a predetermined period when the front wheel of a vehicle travel over a step or a predetermined period when the load acting on the front wheel is changed, is made to resemble the way in which the lateral force (or the rate of change in the lateral force) changes, within a predetermined period when the rear wheel of a vehicle travel over a step or a predetermined period when the load acting on the rear wheel is changed, i.e. if the differences between the two (the front and the rear) changes are decreased, then the possibility exists that the steering characteristics of the vehicle can be adjusted to substantially a neutral state.
More specifically, in the afore-mentioned experiment, the present mode was set as being the mode in which: the rear axle is determined as the reference axle and the front axle is determined as the non-reference axle, when the wheel angle was adjusted so that, after the wheel angle for the reference axle (the rear wheels) was adjusted so that the energy of the variation in the lateral force generated in the tire within a predetermined period which included the time from when the tire was deformed as the wheel traveled over the step until the tire rotated and returned to substantially its normal state was at a minimum, the transition of the lateral force (or rate of change in the lateral force) generated within a predetermined period, which included the time from when the tire was deformed as the wheel traveled over the step until the tire rotated and returned to substantially its normal state, in the wheel of the non-reference axle was similar (i.e. the difference was decreased) to the transition of the reference wheel mounted diagonally opposite each non-reference wheel (i.e. for the right front wheel, the left rear wheel is the diagonally opposite reference wheel, while for the left front wheel, the right rear wheel is the diagonally opposite reference wheel).
Therefore, the present inventors further carried out the experiment described below. Namely, the present inventors used the same vehicles (vehicles 1xcx9c4) and the same tires as in the afore-mentioned experiment, and adjusted the wheel angle of the rear wheel of the reference axle (with the rear axle determined as the reference axle and the front axle determined as the non-reference axle) in the same way as in the afore-mentioned experiment. Then, when adjusting the wheel angle of the front wheel of the non-reference axle (the front wheels), the wheel, mounted on the same side of the vehicle in the transverse direction thereof, of the non-reference axle was taken as the reference wheel (i.e. the right rear wheel was set as the reference wheel for the right front wheel, while the left rear wheel was set as the reference wheel for the left front wheel), and the wheel angle of the wheel of the non-reference axle (the front wheel) was then adjusted in the same way as in the afore-mentioned experiment (the present mode in the Table 3). Experiments were then conducted to compare and evaluate the running stability in this mode with the running stability when the wheel angle of the front wheel and rear wheel of the vehicle were adjusted to the angle determined when the vehicle was designed (the standard mode). The results of the experiment are shown in Table 3. Note that the reference values shown in FIG. 2 are also used for the evaluation value settings in FIG. 3.
As is clear from Tables 1 and 3, on the basis of the results of the above experiments, the present inventors discovered that, if one axle of a plurality of axles of a vehicle (either the front axle or rear axle) is determined to be the reference axle, then if the wheel angle of a wheel mounted on the other axle (non-reference axle) is adjusted so that the transition of the lateral force (or the rate of change in the lateral force) generated in the tire of the wheel (the non-reference wheel) mounted to the other axle (either the front axle or the rear axle) rotating in contact with the road when the tire travels over the step, or when the load acting on the wheel is changed, is similar (the difference is decreased) to the transition of the lateral force (or the rate of change in the lateral force) generated in the tire of the wheel (the reference wheel) mounted to the reference axle (either the front axle or the rear axle) rotating in contact with the road when the tire travels over a step, or when the load acting on the wheel is changed, the result is that, regardless of the type of tire, the steering characteristics of the vehicle can be adjusted to substantially those of neutral steering.
On the basis of the above, in the vehicle wheel alignment adjustment method according to the first aspect of the present invention, a process in which a wheel of the vehicle to be adjusted with a tire fitted thereto is rotated on a wheel rotating surface in a proceeding direction of the vehicle, one of that the wheel passes over a step of a predetermined height formed on the wheel rotating surface or that a (vertical) load acting on the wheel is changed by a predetermined amount within a predetermined period, and a lateral force generated in the tire fitted to the wheel is measured, is performed for a reference wheel having the tire fitted thereto which is mounted on a reference axle of the vehicle, and for a wheel having a tire fitted thereto to be adjusted which is mounted on a non-reference axle of the vehicle,
a comparison is made between a transition of one of the lateral force or a rate of change in the lateral force generated in the tire fitted to the reference wheel and a transition of one of the lateral force or the rate of change in the lateral force generated in the tire fitted to the wheel to be adjusted, and
a wheel-angle of the wheel to be adjusted is adjusted on the basis of the results of the comparison.
According to the first aspect of the present invention, a process in which a wheel of the vehicle to be adjusted with a tire fitted thereto is rotated on a wheel rotating surface in a proceeding direction of the vehicle, one of that the wheel passes over a step of a predetermined height formed on the wheel rotating surface or that a load acting on the wheel is changed by a predetermined amount within a predetermined period, and a lateral force generated in the tire fitted to the wheel is measured, is performed for a reference wheel having the tire fitted thereto which is mounted on a reference axle of the vehicle, and for a wheel having a tire fitted thereto to be adjusted which is mounted on a non-reference axle of the vehicle. Note that, in the present invention, lateral force means the force running in the direction of a line intersecting a plane which includes the axis orthogonal to the proceeding direction (the direction of the relative movement between the vehicle and the wheel rotating surface) of the vehicle and the wheel rotating surface (the road surface). Changing the load acting on the vehicle can be achieved by rotating the wheel on a substantially planar wheel rotating surface and displacing the wheel in a vertical direction via the wheel rotating surface.
Further, in the first aspect of the present invention, a comparison is made between a transition of one of the lateral force or a rate of change in the lateral force generated in the tire fitted to the reference wheel and a transition of one of the lateral force or the rate of change in the lateral force generated in the tire fitted to the wheel to be adjusted, and a wheel angle of the wheel to be adjusted is adjusted on the basis of the results of the comparison. Accordingly, the transition of the lateral force or of the rate of change in the lateral force generated in the tire fitted to the wheel to be adjusted can be brought near to the transition of the lateral force or of the rate of change in the lateral force generated in the tire fitted to the reference wheel. Therefore, as is clear also from the results of the experiment described above, the wheel angle can be adjusted to an wheel angle in accordance with the characteristics of the tire so as to make the steering characteristics of the vehicle substantially the characteristics of neutral steer.
It is preferable that the period for comparing the transitions of the lateral force or of the rates of change in the lateral force is the period which includes the time from when the tire deforms as the wheel travels over the step or as the load acting on the wheel is changed until the tire rotates and returns substantially to its normal state. This period can be determined by, for example, detecting the start of the period by detecting the displacement of the wheel and then detecting the end of the period by measuring a certain passage of time since the start of the period. However, in this case, a complicated mechanism is necessary to determine the period for comparing the transitions of the lateral force or of the rates of change in the lateral force and errors may occur in determining the period.
For this reason, in the vehicle wheel alignment adjustment method according to the second aspect of the present invention, a process in which a wheel of the vehicle to be adjusted with a tire fitted thereto is rotated on a wheel rotating surface in a proceeding direction of the vehicle, one of that the wheel passes over a step of a predetermined height formed on the wheel rotating surface or that a load acting on the wheel is changed by a predetermined amount within a predetermined period, and one of a longitudinal force or a (vertical) load, and a lateral force generated in the tire fitted to the wheel are each measured, is performed for a reference wheel having the tire fitted thereto which is mounted on a reference axle of the vehicle, and for a wheel having a tire fitted thereto to be adjusted which is mounted on a non-reference axle of the vehicle,
a predetermined period including a time from when the tire of the wheel is deformed at one of the wheel passing over a step or the load acting on the wheel being changed until the tire rotates and returns substantially to normal state is determined for the reference wheel and for the wheel to be adjusted on the basis of the results of the measurement of one of the longitudinal force or the load,
a comparison is made between a transition of one of the lateral force or a rate of change in the lateral force generated in the tire fitted to the reference wheel and a transition of one of the lateral force or the rate of change in the lateral force generated in the tire fitted to the wheel to be adjusted within the predetermined period, and
a wheel angle of the wheel to be adjusted is adjusted on the basis of the results of the comparison.
In the second aspect of the present invention, a process in which a wheel of the vehicle to be adjusted with a tire fitted thereto is rotated on a wheel rotating surface in a proceeding direction of the vehicle, one of that the wheel passes over a step of a predetermined height formed on the wheel rotating surface or that a load acting on the wheel is changed by a predetermined amount within a predetermined period, and one of a longitudinal force or a load, and a lateral force generated in the tire fitted to the wheel are each measured, is performed for a reference wheel having the tire fitted thereto which is mounted on a reference axle of the vehicle, and for a wheel having a tire fitted thereto to be adjusted which is mounted on a non-reference axle of the vehicle, a predetermined period including a time from when the tire of the wheel is deformed at one of the wheel passing over a step or the load acting on the wheel being changed until the tire rotates and returns substantially to normal state is determined for the reference wheel and for the wheel to be adjusted on the basis of the results of the measurement of one of the longitudinal force or the load. Note that the longitudinal force according to the present invention is the force in a direction running along a line intersecting a plane which includes the axis running in the direction in which the vehicle travels forward (the direction in which the vehicle moves relative to the wheel rotating surface) and the wheel rotating surface (the road surface), while the load according to the present invention is the force in a vertical direction applied to the wheel rotating surface (the road surface).
The longitudinal force and the load can both be easily measured by providing a sensor on the wheel rotating surface, a member connected to the wheel rotating surface, or on the wheel which is to be adjusted (in the same way as the lateral force). Moreover, provided that the vehicle is the same, the transition of the longitudinal force and the load generated in the tire (i.e. the waveform) as the wheel rotates and travels over the step and the load acting on the wheel is changed undergo almost no change even if the alignment of the wheel is altered. Accordingly, a predetermined period can be accurately determined by basing the determination on the results of the measurement of the longitudinal force or the load, even when the lateral force and the longitudinal force or the load is measured and the wheel angle is adjusted repeatedly.
Note that, as described above, when the load acting on the wheel is changed by the wheel being displaced in the vertical direction via the wheel rotating surface, the longitudinal force generated in the tire does not exhibit clear changes for the tire. Because of this, when the load acting on the vehicle is changed by displacing the wheel via the wheel rotating surface, the predetermined period may be determined by measuring both the load and the lateral force generated in the tire fitted to the wheel and comparing the results of the measurement with the load generated in the tire when the tire fitted to the wheel is substantially its normal state.
In the second aspect of the present invention, a comparison is made between a transition of one of the lateral force or a rate of change in the lateral force generated in the tire fitted to the reference wheel and a transition of one of the lateral force or the rate of change in the lateral force generated in the tire fitted to the wheel to be adjusted within the predetermined period, and
a wheel angle of the wheel to be adjusted is adjusted on the basis of the results of the comparison. Therefore, as in the first aspect of the present invention, the wheel angle can be adjusted to an wheel angle in accordance with the characteristics of the tire so as to enable the steering characteristics of the vehicle to be set at substantially neutral steer.
Note that, according to the first and second aspects of the present invention, it is preferable to adjust the wheel angle of the reference wheel in advance. It is also preferable that the adjustment of the wheel angle of the reference wheel alignment be carried out in the following manner.
In the third aspect of the present invention, according to the first and second aspects of the present invention, the reference wheel is rotated on a wheel rotating surface in the proceeding direction of the vehicle, one of that the reference wheel passes over the step of the predetermined height formed on the wheel rotating surface or that the load acting on the reference wheel is changed by the predetermined amount in the predetermined period, and the lateral force generated in the tire fitted to the reference wheel is measured; and
the wheel angle of the reference wheel is adjusted in advance so that an energy of a variation in the lateral force generated in the tire within the predetermined period which includes the time from when the tire of the reference wheel is deformed atone of the reference wheel passing over the step or at the load acting on the reference wheel being changed until the tire rotates and returns to substantially normal state is within a predetermined range which includes the minimum value of the energy of the vibration.
In the third aspect of the present invention, the reference wheel is rotated on a wheel rotating surface in the proceeding direction of the vehicle, one of that the reference wheel passes over the step of the predetermined height formed on the wheel rotating surface or that the load acting on the reference wheel is changed by the predetermined amount in the predetermined period, and the lateral force generated in the tire fitted to the reference wheel is measured; and the wheel angle of the reference wheel is adjusted in advance so that an energy of a variation in the lateral force generated in the tire within the predetermined period which includes the time from when the tire of the reference wheel is deformed atone of the reference wheel passing over the step or at the load acting on the reference wheel being changed until the tire rotates and returns to substantially normal state is within a predetermined range which includes the minimum value of the energy of the vibration. (e.g. the predetermined range is a range from the minimum value to a predetermined value). preferably, the wheel angle is adjusted so that the energy of the variation in the lateral force is the minimum in the adjustable range of the vehicle to be adjusted. However, there are also vehicles whose energy of the variation in the lateral force cannot be adjusted to the minimum because the wheel angle adjustment pitch (the value of the smallest changeable angle) is at variance due to the type of model (structure) and the like of the vehicle to be adjusted.
Accordingly, as is also clear from Tables 1 and 3, the alignment (wheel angle) of the reference wheel is easily adjusted to an alignment which accords with the characteristics of the tire. Thus a running stability suitable for an actual road surface and a reduction in one-sided wear can both be achieved. Further, in the third aspect of the present invention, because the alignment of the reference wheel is adjusted on the basis of the energy of the variation in the lateral force generated in the tire within the predetermined period which includes the time from when the tire of the reference wheel is deformed as the reference wheel travels over the step or as the load acting on the reference wheel is changed until the tire rotates and returns to substantially its normal state, compared to when the alignment of the reference wheel is adjusted on the basis of the lateral force during the time the longitudinal force generated in the tire is at the maximum value or close to the maximum value, there is no reduction in the precision of the adjustment of the alignment of the reference wheel due to the effects of the suspension geometry of the vehicle, as is disclosed in JP-A No. 10-7013.
By adjusting the wheel angle of the wheel to be adjusted (the non-reference wheel) according to the adjustment method according to the first or second aspects of the present invention, the front and rear balance of the vehicle is optimized and a state of substantially neutral steer is achieved, and the wheel to be adjusted is adjusted in accordance with the tire characteristics, leading to an improvement in both running stability and one-sided wear.
In the fourth aspect of the present invention, according to the first or second aspects of the present invention, the reference wheel and the wheel to be adjusted whose transitions of one of the lateral force or the rate of change in the lateral force are compared are wheels mounted on the vehicle at positions diagonally opposite to each other. In the fourth aspect of the present invention, one of the two wheels which are mounted on the vehicle at positions diagonally opposite to each other and whose transitions of the lateral force or of the rate of change in the lateral force are compared is the reference wheel and the other of the two wheels is the wheel to be adjusted. Therefore, as is clear also from a comparison of the results of the experiment shown in Tables 1 and 3, in general running conditions such as when driving in a substantially straight line or on a circuit where no great sideways acceleration is present, a better straight line stability and cornering stability performance can be obtained.
FIG. 2 shows the transition of the primary differential value (dFx/dt) in relation to the time t of the longitudinal force Fx and the primary differential value (dFy/dt) in relation to the time t of the lateral force Fy when the longitudinal force Fx and the lateral force Fy are measured by a method in which a step (an upward step and downward step) is formed in a wheel rotating surface by providing a planar-like protrusion, such as that described in the fourth aspect, and the vehicle and wheel rotating surface are moved relative to each other in such a way that the wheel rotates on the wheel rotating surface in the direction in which the vehicle moves forward and travels over the protrusion (travels over the upward step, rotates over the top surface of the protrusion (the protruding surface), and then travels down the downward step). FIG. 3 shows the transition of the primary differential value (dFz/dt) in relation to the time t of the load Fz and the primary differential value (dFy/dt) of the lateral force Fy when the load Fz and the lateral force Fy are measured under the same conditions as for FIG. 2.
Note that the (two) locations in FIG. 2 where the primary differential value of the longitudinal force suddenly undergoes a huge change in the positive or negative direction and the (two) locations in FIG. 3 where the primary differential value of the load suddenly undergoes a huge change in the positive or negative direction indicate the variation in the longitudinal force and the load caused by the deformation of the tire which occurs when the wheel travels over the upward step or the downward step. The area between the locations in FIGS. 2 and 3 where the primary differential value of the longitudinal force and the primary differential value of the load undergo a huge change corresponds to when the wheel is rotating on the top surface of the protrusion (the protruding surface) and the tire is in the process of returning to substantially its normal state, and, as is clear from FIGS. 2 and 3, the primary differential value of the longitudinal force and the primary differential value of the load are still changing during this time, even if only slightly. Consequently, in order to determine from the longitudinal force or the load (or from the primary differential value of the longitudinal force or load) whether the tire has returned to substantially its normal state when the longitudinal force or load are measured by forming a step of a predetermined height on a wheel rotating surface and rotating a wheel with the tire fitted thereon so that the wheel travels over the step, easier, the six aspect of the present invention is provided.
Because of this, in the fifth aspect of the present invention, according to the second aspect of the present invention, the step is formed on the wheel rotating surface by providing on the wheel rotating surface a substantially plate shaped protrusion whose top surface is a predetermined height above a base surface of the wheel rotating surface, and the protrusion is formed so that the protruding surface extends long enough in a direction of a relative movement of the vehicle and the wheel rotating surface for both ends of a ground-contacting portion of the tire in the direction of the relative movement to be in contact with the protruding surface when the wheel passes over the protrusion, and
the predetermined period is determined to be a period from a first timing until a second timing, the first timing is when a rate of a change at least one of in the longitudinal force or the load as the wheel climbs up onto the protrusion with the tire of the wheel deforming becomes the minimum after changing to a predetermined value or more, the second timing is one of when the rate of the change at least one of in the longitudinal force or the load becomes to the minimum after changing to a predetermined value or more, or when a front end of the ground-contacting portion of the tire in the direction of the relative movement is without contacting with the protruding surface as the tire rotates on the protruding surface and the wheel descends from the protrusion with the tire of the wheel deforming.
In the sixth aspect of the present invention, the time when the rate of the change (the primary differential value) of the longitudinal force or load caused by the tire on a wheel deforming as the wheel climbs up onto the protrusion becomes the minimum (for example, substantially xe2x80x9c0xe2x80x9d) after changing to a predetermined value or more is taken as the first timing (the timing indicated by P1 in FIGS. 2 and 3), and the time when the rate of the change in the longitudinal force or the load caused by the tire on a wheel deforming as the wheel descends from the protrusion after the tire has rotated on the protruding surface becomes the minimum (namely, substantially xe2x80x9c0xe2x80x9d) after changing to a predetermined value or more (the timing indicated by P2 in FIGS. 2 and 3), or the time when the front end of the ground-contacting portion of the tire in the direction of the relative movement is not in contact with the protruding surface (for example, the timing which corresponds to the peak of the portion of the primary differential value of the longitudinal force or load changing to a predetermined value or more immediately before P2) is taken as the second timing. Because the period from the first timing until the second timing is determined to be the predetermined period, the first timing and second timing can be determined easily and with a high degree of accuracy from the results of the measurement of the longitudinal force or load, thus enabling the predetermined period to be determined with a high degree of accuracy. (the wheel is the reference wheel and the wheel to be adjusted.)
In the sixth aspect of the present invention, according to the second aspect of the present invention, a wave form of one of the lateral force or the rate of change in the lateral force generated in the tire of the reference wheel within the predetermined period and a wave form of one of the lateral force or the rate of change in the lateral force generated in the tire of the wheel to be adjusted within the predetermined period are compared to obtain the difference between the two wave forms, and
the wheel angle of the wheel to be adjusted is adjusted in such a way that the difference between the two wave forms is reduced.
Note that, according to the second aspect of the present invention, the wave form of the lateral force or the rate of change in the lateral force generated in the fire fitted to the reference wheel within the predetermined period and the wave form of the lateral force or the rate of change in the lateral force generated in the tire fitted to the wheel to be adjusted within the predetermined period are compared to obtain the difference between the two wave forms and the adjustment of the alignment of the wheel to be adjusted is performed in such a way that the difference between the two wave forms is reduced (in such a way that two wave form substantially coincidence), as is described specifically in the sixth aspect of the present invention.
Because, generally, a caster angle is imparted to the front wheel of a vehicle, the timing when the longitudinal force or load is greatly changed (for example, by a predetermined amount or more) due to the tire fitted to the wheel deforming as the wheel travels over the step or as the load acting on the wheel is changed is often different for the front wheel and the rear wheel of the vehicle. Therefore, in the seventh aspect of the present invention, according to the sixth aspect of the present invention, a characteristic point is extracted from the wave form of the lateral force or the rate of change in the lateral force generated in the of the reference wheel within the predetermined period and a characteristic point is extracted from the wave form of the lateral force or the rate of change in the lateral force generated in the tire of the wheel to be adjusted within the predetermined period, the two wave forms are superposed with the characteristic points superposed as a reference point so as to obtain the difference in the two wave forms.
Note that, for example, the characteristic occurring in the waveform of the lateral force or of the rate of change in the lateral force when the relative positions of the wheel and the step are substantially a predetermined position can be used as the characteristic point described in the seventh aspect of the present invention. In the seventh aspect of the present invention, because the characteristic point is extracted from the wave form of the lateral force or the rate of change in the lateral force generated in the tire fitted to the reference wheel within the predetermined period and the characteristic point is extracted from the wave form of the lateral force or the rate of change in the lateral force generated in the tire fitted to the wheel to be adjusted within the predetermined period, and the two wave forms are then superposed with the characteristic points superposed as a reference point to obtain the difference in the wave forms, the wave forms of the reference wheel and the wheel to be adjusted can be superposed with the relative position of the wheel and the step as a reference. Accordingly, even if the timing when the longitudinal force or load generated in the tire is changed by a predetermined amount or more is different for the front wheel and the rear wheel of the vehicle, the steering characteristics of the vehicle can be precisely adjusted to substantially neutral steer characteristics.